The present invention relates to a hybrid magnetic bubble memory device, i.e. a magnetic bubble memory device in which magnetic bubble propagation tracks formed through ion implanation and magnetic bubble propagation tracks formed of a soft magnetic material exemplified by permalloy (Ni-Fe alloy) are coexistent in a single chip. More especially, the present invention relates to the propagation tracks of soft magnetic material in such a hybrid device.
At present, magnetic bubble propagation tracks formed of permalloy is widely employed as the bubble propagation track in the magnetic bubble memory device. However, high density propagation tracks of permalloy having a periodicity not larger than 4 .mu.m can afford only a small propagation margin and is not suited for practical applications. In contrast, it is known that ion-implanted propagation tracks formed through ion implanation by means of a gapless pattern is practically suited for realizing high density propagation tracks of a periodicity not larger than 4 .mu.m. Details of ion-implanted bubble propagation tracks are disclosed in T. J. Nelson el, "Design of Bubble Device Elements Employing Ion-Implanted Propagation Patterns", The Bell System Technical Journal, Vol. 59, No. 2, pp. 229-257. However, the ion-implanted propagation tracks are not yet practically employed in the magnetic bubble memory device because functional parts such as replicate gates, swap gates and others which are requisite for the magnetic bubble memory device do not operate satisfactorily. As to these functional parts, an adequate operation margin can be accomplished by employing the permalloy propagation tracks. Accordingly, it may be said that a so-called hybrid magnetic bubble memory device in which a storage area occupying the most part of the chip area is realized by the ion-implanted propagation tracks while the functional parts are realized by the permalloy propagation tracks, is suited for realization with an increased density. For particulars of such a hybrid magnetic bubble memory device, reference may be made to Japanese Patent Application Laid-Open No. 57-40791 laid open in 1982.
A structure of the hybrid device is shown in FIG. 1 of the accompanying drawings. In the figure, the permalloy propagation tracks are represented by portions 1 depicted in solid lines, while the ion-implanted propagation tracks are represented by broken line portions 2. A region 3 enclosing therein the ion-implanted tracks 2 is implanted with ions on the same condition for realizing the ion-implanted propagation tracks 2. On the other hand, a region 4 extending around the ion-implanted region 3 and including the permalloy propagation tracks 1 is not implanted with ions or is shallowly implanted under an ion implanting condition different from that for the region 3 and for the purpose of suppressing generation of hard bubbles. In FIG. 1, reference numeral 5 denotes a magnetic bubble generator and numeral 6 denotes a magnetic bubble detector.
In the hybrid device of the structure mentioned above, importance is put on the range of operation of the magnetic bubbles for each of the ion-implanted propagation track and the permalloy propagation track in the regions 3 and 4 which are formed under the different ion-implanting conditions.
FIG. 2 illustrates the operation ranges of the ion-implanted propagation track having a periodicity of 8 .mu.m and the permalloy propagation track having a periodicity of 16 .mu.m when that magnetic bubbles having a diameter of 2 .mu.m are made use of. As will be seen from this figure, the operation ranges of both the propagation tracks for the 2 .mu.m diameter bubbles are substantially coincident with each other, giving rise to no problem. However, when the magnetic bubbles of a diameter smaller than 1 .mu.m, e.g. 0.5 .mu.m are used in the case where the periodicities of the ion-implanted and permalloy propagation tracks are same as the above, it has been found that the operation range of the bubble in the permalloy propagation track is shifted to a higher region of the bias magnetic field as compared with that in the ion-implanted propagation track and has also the decreased width, as will be seen from FIG. 3. For these reasons, a great difficulty has been encountered in assuring the operation range of the magnetic bubble common to both type of the propagation tracks, involving difficulty in realizing a high reliable hybrid device.